Investigation of parametric effects using small colour differences

This experiment was carried out to investigate some viewing parameters affe cting perceived colour differences. It was divided into eight phases. Each phase was conducted under a different set of experimental conditions includ ing separations, neutral backgrounds, and psychophysical methods. Seventy-J ive wool sample pairs were prepared corresponding to five CIE colour center s. The mean colour difference was three CIELAB units. Each pair was assesse d by a panel of 21 observers using both the gray scale and pair comparison psychophysical methods. The assessments were carried out using the three di fferent back grounds (white, mid-gray, and black) and a hairline gap betwee n the samples. Assessments on the gray background were repeated using a lar ge (3-inch) gap between the samples. It was found that the visual results o btained from both psychophysical methods gave very similar results. The par ametric effect was small, i.e., the largest effect was only 14% between the white and gray background conditions. These visual data were also used to test four colour-difference formulae: CIELAB, CMC, BFD, and CIE94. The resu lts showed that three advanced colour-difference formulae performed much be tter than CIELAB. There was a good agreement between the current results an d those from earlier studies. (C) 1999 John Wiley & Sons, Inc.